The basic principles and the concept of two-dimension gas chromatography ((GC×GC)) have been well established. The modulator is considered as the key component of ((GC×GC)) supported by an appropriate choice of conditions and columns. Its main functions are to: 1) repeatedly accumulate or trap narrow “zones” of the effluent from the first dimension (1D) column; 2) refocus, and, 3) release the collected effluent into the second dimension (2D) column. Rapid sampling allows the original 1D column separation to be approximately preserved. The 2D column separation is optimally completed before the next release of a accumulated 1D column effluent in order to minimize wrap-around (i.e., the overlap of adjacent 1D effluent samples in the 2D column). This is typically achieved by performing the 2D column separation in just a few seconds (e.g., 2-12 sec). The time constraints on the 2D separation are not conducive to temperature gradients. Therefore the 2D column separation is generally limited to isothermal conditions.
The isothermal separation of complex samples by GC suffers from the general elution problem in which the first peaks are not fully-resolved and the later eluting peaks are spread and broad. As a result, typical (GC×GC) chromatograms do not take advantage of the entire second dimension space. A conventional solution to the general elution problem is programmed temperature gradient gas chromatography (PTGC). However, the application of PTGC in the second dimension is constrained due to the short analysis time available (<12 sec).
Accordingly, a need exists for better (GC×GC) systems and methods that allow rapid temperature cycling of the 2D column, thereby facilitating programmed temperature gradient gas chromatography (PTGC) in the 2D column and better separation of complex samples without causing wraparound of 1D samples or necessitating the use of multiple second dimension columns.